--- type: "thread-series" series: "npt" name: "NPT Taper Pipe Thread" system: "pipe" size_count: 24 smallest: "1/16-27 NPT" largest: "24-8 NPT" standard: "ASME B1.20.1, ASME B1.20.3; public-domain primary FED-STD-H28/7A (1984)" verified: "August 1, 2026" url: https://shopmath.org/threads/npt --- # NPT Taper Pipe Thread Thread Chart — All 24 Sizes, Dimensions & Tap Drills The NPT Taper Pipe Thread series covers 24 standard sizes, from 1/16-27 NPT to 24-8 NPT, and 24 of them carry a tap drill recommendation. American National Standard taper pipe thread, ASME B1.20.1 — sealing needs a compound or tape. - **Sizes**: 24 - **Smallest**: 1/16-27 NPT - **Largest**: 24-8 NPT - **Standard**: ASME B1.20.1, ASME B1.20.3; public-domain primary FED-STD-H28/7A (1984) ## Every NPT Thread Size — Dimensions and Tap Drills Ordered smallest to largest. Every row links to the full page for that thread, with class limits, clearance holes and tap drills across 50–85% engagement. | Thread | TPI | Major Ø (in) | Major Ø (mm) | Pitch Ø (in) | Pitch Ø (mm) | Minor Ø (in) | Minor Ø (mm) | Tap drill | Tap drill Ø (in) | Tap drill Ø (mm) | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | [1/16-27 NPT](https://shopmath.org/threads/npt/1-16.md) | 27 | 0.3125 | 7.938 | 0.2812 | 7.142 | 0.2516 | 6.391 | E | 0.2500 | 6.350 | | [1/8-27 NPT](https://shopmath.org/threads/npt/1-8.md) | 27 | 0.4050 | 10.287 | 0.3736 | 9.489 | 0.3440 | 8.738 | 11/32 | 0.3438 | 8.731 | | [1/4-18 NPT](https://shopmath.org/threads/npt/1-4.md) | 18 | 0.5400 | 13.716 | 0.4916 | 12.487 | 0.4472 | 11.359 | 7/16 | 0.4375 | 11.113 | | [3/8-18 NPT](https://shopmath.org/threads/npt/3-8.md) | 18 | 0.6750 | 17.145 | 0.6270 | 15.926 | 0.5826 | 14.798 | 37/64 | 0.5781 | 14.684 | | [1/2-14 NPT](https://shopmath.org/threads/npt/1-2.md) | 14 | 0.8400 | 21.336 | 0.7784 | 19.772 | 0.7213 | 18.321 | 23/32 | 0.7188 | 18.256 | | [3/4-14 NPT](https://shopmath.org/threads/npt/3-4.md) | 14 | 1.0500 | 26.670 | 0.9889 | 25.117 | 0.9317 | 23.665 | 59/64 | 0.9219 | 23.416 | | [1-11.5 NPT](https://shopmath.org/threads/npt/1.md) | 12 | 1.3150 | 33.401 | 1.2386 | 31.461 | 1.1691 | 29.695 | 1 | 1.0000 | 25.400 | | [1 1/4-11.5 NPT](https://shopmath.org/threads/npt/1-1-4.md) | 12 | 1.6600 | 42.164 | 1.5834 | 40.218 | 1.5138 | 38.450 | 1 | 1.0000 | 25.400 | | [1 1/2-11.5 NPT](https://shopmath.org/threads/npt/1-1-2.md) | 12 | 1.9000 | 48.260 | 1.8223 | 46.287 | 1.7528 | 44.521 | 1 | 1.0000 | 25.400 | | [2-11.5 NPT](https://shopmath.org/threads/npt/2.md) | 12 | 2.3750 | 60.325 | 2.2963 | 58.325 | 2.2267 | 56.558 | 1 | 1.0000 | 25.400 | | [2 1/2-8 NPT](https://shopmath.org/threads/npt/2-1-2.md) | 8 | 2.8750 | 73.025 | 2.7622 | 70.159 | 2.6622 | 67.620 | 1 | 1.0000 | 25.400 | | [3-8 NPT](https://shopmath.org/threads/npt/3.md) | 8 | 3.5000 | 88.900 | 3.3885 | 86.068 | 3.2885 | 83.528 | 1 | 1.0000 | 25.400 | | [3 1/2-8 NPT](https://shopmath.org/threads/npt/3-1-2.md) | 8 | 4.0000 | 101.600 | 3.8888 | 98.776 | 3.7888 | 96.236 | 1 | 1.0000 | 25.400 | | [4-8 NPT](https://shopmath.org/threads/npt/4.md) | 8 | 4.5000 | 114.300 | 4.3871 | 111.433 | 4.2871 | 108.892 | 1 | 1.0000 | 25.400 | | [5-8 NPT](https://shopmath.org/threads/npt/5.md) | 8 | 5.5630 | 141.300 | 5.4493 | 138.412 | 5.3493 | 135.872 | 1 | 1.0000 | 25.400 | | [6-8 NPT](https://shopmath.org/threads/npt/6.md) | 8 | 6.6250 | 168.275 | 6.5060 | 165.252 | 6.4060 | 162.712 | 1 | 1.0000 | 25.400 | | [8-8 NPT](https://shopmath.org/threads/npt/8.md) | 8 | 8.6250 | 219.075 | 8.5000 | 215.901 | 8.4000 | 213.360 | 1 | 1.0000 | 25.400 | | [10-8 NPT](https://shopmath.org/threads/npt/10.md) | 8 | 10.7500 | 273.050 | 10.6209 | 269.772 | 10.5209 | 267.231 | 1 | 1.0000 | 25.400 | | [12-8 NPT](https://shopmath.org/threads/npt/12.md) | 8 | 12.7500 | 323.850 | 12.6178 | 320.492 | 12.5178 | 317.952 | 1 | 1.0000 | 25.400 | | [14-8 NPT](https://shopmath.org/threads/npt/14.md) | 8 | 14.0000 | 355.600 | 13.8726 | 352.365 | 13.7726 | 349.824 | 1 | 1.0000 | 25.400 | | [16-8 NPT](https://shopmath.org/threads/npt/16.md) | 8 | 16.0000 | 406.400 | 15.8758 | 403.244 | 15.7758 | 400.705 | 1 | 1.0000 | 25.400 | | [18-8 NPT](https://shopmath.org/threads/npt/18.md) | 8 | 18.0000 | 457.200 | 17.8750 | 454.025 | 17.7750 | 451.485 | 1 | 1.0000 | 25.400 | | [20-8 NPT](https://shopmath.org/threads/npt/20.md) | 8 | 20.0000 | 508.000 | 19.8703 | 504.706 | 19.7703 | 502.166 | 1 | 1.0000 | 25.400 | | [24-8 NPT](https://shopmath.org/threads/npt/24.md) | 8 | 24.0000 | 609.600 | 23.8609 | 606.068 | 23.7609 | 603.527 | 1 | 1.0000 | 25.400 | _Basic dimensions are the theoretical values before a tolerance class is applied. Tap drills are for cut taps at the default engagement; per-size pages carry 50–85%._ ## Sources and Method for the NPT Thread Chart ### NPT thread dimensions - **Source**: ASME B1.20.1 taper pipe thread formulas; E0 and L2 reproduced to 5 decimals in docs/research/data-sourcing.md §3.3. Public-domain primary: FED-STD-H28/7A (1984).; pipe OD / tpi / L1 / L4: ASME B1.20.1 pipe OD / tpi / L1 / L4 via Wikipedia National pipe thread (CC BY-SA 4.0); OD and tpi cross-checked against FreeCAD FeatureHole.cpp NPT block (LGPL-2.1+) - **Method**: computed+compiled - **Verified against**: Wikipedia National pipe thread standard-sizes table (CC BY-SA 4.0) — 98 checks passed to 1e-5 in ### Assumptions - Tap drill figures are for cut taps at the default thread engagement; each size page carries the full 50–85% range. - Dataset scope: L1 is tabulated, not derivable (data-sourcing.md §3.3). EXCLUDED: NPTF crest/root truncation limits (single-sourced), NPSM/NPSC/NPSF straight pipe threads, BSPT/BSPP. **Data last verified**: August 1, 2026 ## Related pages - Every thread series: [Screw thread reference](https://shopmath.org/threads.md) - Cross-series chart: [Tap drill chart](https://shopmath.org/charts/tap-drill.md) - Drill index: [Drill size chart](https://shopmath.org/charts/drill-sizes.md) --- *Source: [ShopMath](https://shopmath.org/threads/npt) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*